[presto8]

or, more neutrally: "myusername has not listed their skills."

This is incorrect grammar (the subject and pronoun should agree)! Something like "myusername's skills have not been listed" would be ok.

[aphyr]

"Their" is totally a gender-neutral 3nd person singular now.

[sesqu]

Now? It's been a gender-neutral 3rd person singular for hundreds of years.

[cormullion]

More than you want to read about this:

http://languagelog.ldc.upenn.edu/nll/?cat=27

[jackowayed]

That's awkward passive voice. How about "myusername has not listed skills"?

[trouble]

What about "myusername has not listed any skills."?

[kaerast]

Or "myusername has no skills". That way you encourage people to add their skills.

[chrisaycock]

Shorter: "myusername has no listed skills."

[WingForward]

"myusername has listed no skills" sounds better to my ear.

[prawn]

Doesn't cater for users who only have one skill to list. ;)